Image display panel

ABSTRACT

This disclosure depicts a video image display panel having improved light-emissive elements each comprising a first gas discharge cell which is excited by an applied video signal sample and which emits radiation in proportion to the applied signal. The photons emitted by the first cell stimulate an image intensifying stage. The image-intensifying stage includes a photoconductive element and a light-emissive gas discharge cell capable of emitting light or selected color at relatively high efficiency. In one disclosed embodiment the storage capability of the photoconductive element is maximized and augmented by storing the video signal sample which is applied to the stimulated gas discharge cell.

United States Patent De Jule July 31, 1973 IMAGE DISPLAY PANEL Michael C. De Jule, Chicago, 111.

Zenith Radio Corporation, Chicago, 111.

Filed: Apr. 27, 1972 Appl. No.: 248,322

Inventor:

Assignee:

U.S. Cl 315/169 TV, 313/109.5, 315/169 R Int. Cl. 1105b 37/00 Field of Search 313/1095, 217, 220;

References Cited UNITED STATES PATENTS 11/1971 315/169 TV 5/1972 315/169 TV Kupsky Lustig Primary ExaminerRoy Lake Assistant ExaminerLawrence J. Dahl Attornev-John H. Coult and John J. Pederson [57] ABSTRACT This disclosure depicts a video image display panel having improved light-emissive elements each comprising a first gas discharge cell which is excited by an applied video signal sample and which emits radiation in proportion to the applied signal. The photons emitted by the first cell stimulate an image intensifying stage. The image-intensifying stage includes a photoconductive element and a light-emissive gas discharge cell capable of emitting light or selected color at relatively high efficiency. In one disclosed embodiment the storage capability of the photoconductive element is maximized and augmented by storing the video signal sample which is applied to the stimulated gas discharge cell.

11 Claims, 1 Drawing Figure Row Drivers Reset & Memory and Control 7 Column Drivers 1 1 p 46 Vertical- Hosrlzontcl i C I nc 0 mn Sync Horizontal Video ge|ecuting 5'- Sync Sampling nd Detector Switch Driving A System 48 k 44 Video Video In Ampiifler IMAGE DISPLAY PANEL BACKGROUND OF THE INVENTION This application concerns video display panels of the type comprising an X-Y matrix of light-emissive elements which are addressed by means of rows and columns of conductors. X-Y addressed display panels using binary gas discharge cells as the luminescent elements are well known. Such panels exploit the favorable threshold properties of gas discharge cells which enable the cells in the X-Y matrix to be addressed and excited individually. Such panels may be suitable for application in numeric display systems and other binary devices, however, their relatively low efficiency and brightness and their lack of sufficient gray-scale capability and color selectability have made them generally unsuitable for displaying video information.

This application addresses three problem areas lying in the path of a commercially viable gas discharge television display paneli namely, (1) efficiency, (2) brightness, and (3) color selectability.

PRIOR ART The following are considered to be prior art: An Experimental 4,000 Picture Element Gas Discharge TV Display Panel" by Th. J. deBoer,; Flat Screen Television Takes Two Giant Steps Forward, appearing in Electronics, May 25, 1970; US. Pat. Nos. 3,479,517 Bray, et al.; 3,629,638 Vernon, et al.; 2,967,965 Schwartz; 3,619,700 Kupsky; and 3,617,796 Caras.

OBJECTS OF THE INVENTION It is a general object of this invention to provide an improved optical display panel, especially a video image display panel having improved light-emissive elements. It is a less general object to provide a video display panel having light-emissive elements which are capable of producing relatively high brightness and efficiency and selectability in the spectral characteristics of emitted light.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a fragmentary view, partially schematic, of an image display panel embodying the teachings of this invention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawing illustrates a portion of a video image display panel having a matrix of light-emissive elements embodying the teachings of this invention.

In accordance with the invention, in a general sense, light-emissive elements are provided which comprises radiation-emissive image-forming means for emitting photons in proportion to an applied video signal sample. The image-forming means may be thought of as collectively forming an image which may be binary or may be a video image having continuous tone, but which is relatively weak. An image intensifier stage is optically coupled to the image-forming means for producing an intensified display image and, in a preferred embodiment, for imparting a predetermined color to the display image.

The image-intensifying means includes photoconductive means optically coupled to the image-forming means, a luminescent gas discharge display cell electrically coupled to, but optically isolated from, the photoconductive means, and means for applying a potential across the display cell and the photoconductive means such that the power applied to the display cell varies in accordance with changes in the level of radiation emitted by said radiation emissive means (and thus with changes in the video signal). The photoconductive means acts to store the video signal for a storage period which is substantially longer than the period of stimulation thereof.

In more detail, the illustrated preferred embodiment, the radiation-emissive image-forming means collectively function to develop an image hereinafter termed a latent image, which may be either visible or invisible to the human eye, having appropriate gray-scale values to enable the rendition of a continuous tone picture. The image-forming means also functions, either by itself or in association with external circuitry, to accomplish the threshold switching necessary in an X-Y matrix-type panel to enable activation of a selected display element without partially exciting other elements in either the selected row or selected column.

The image-forming means may take many forms capable of satisfying these dual functions. For example, it may take the form of an electroluminescent cell, a valving cell for controlling transmission of light generated by an external source of illumination, or a number of other suitable light control elements capable of emitting or passing photons in proportion to a signal applied thereto. The radiation emitted by the image-forming means may be visible or ultraviolet or infa-red light, gamma rays, electrons or other suitable radiation capable of stimulating a photoconductive element to be described in detail below. The image-forming means is, according to this invention, preferably a luminescent gas discharge cell.

FIG. 1 illustrates a fragment of a video display panel having a large number of gas discharge image cells 10 arranged in rows and columns to form a matrix. Each image cell is illustrated as being formed as a cylindrical cavity 12 in an electrically insulative cavity plate 14. Insulative inner and outer cover plates 16, I8 hermetically sealed with the top and bottom surfaces of the plate 14 close the ends of the cavity 12.

An array of wire-like column and row electrodes, hereinafter described as image anodes 20" and image cathodes 22 respectively, are provided for exciting ionizable gases in the image cells 10. The image anodes and cathodes 20, 22 are here shown as being recessed in notches 24, 26 in the cavity plate 14 to permit the cover plates 16, 18 to make an intimate seal therewith. Before sealing, the cavities 12 are charged with an ionizable gas at an appropriate pressure. Suitable gases include (but are not limited to) neon, xenon, krypton, and mixtures of these with or without additives.

The inner cover plate 18 is preferably composed of glass or other suitable optically transparent material to permit optical coupling with certain succeeding layers of the panel (to be described), while electrically insulating the image cell 10 from succeeding layers. Row and column selection and driving peripheral circuitry for exciting cells 10 to photon emission will be described in detail below after a discussion of the remaining components of the light-emissive elements 8.

The above-described matrix of image cells 10 for developing a latent image provide an element selection capability and a capability for providing a luminous output which varies in accordance with excitation thereof, i.e., a multiple gray level capability. In accordance with this invention, the matrix of image cells are not taxed with providing high luminous output or color selectability. According to this invention, each element 8 includes light-intensifying means for achieving these functions.

In the illustrated embodiment the ight-intensifying means is depicted as comprising a photoconductive layer 28 which is optically coupled to the image cell 10 through the optically transparent inner cover plate 18. The photoconductive layer 28 is sensitive to photons emitted by the image cell 10. The image cell 10 and photoconductive layer 28 are preferably chosen and constructed such as to maximize the optical coupling there between. The photoconductive layer 28 is of such character as to have an impedance which varies with the number of photons impinging thereon and which maintains impedance resulting from photon stimulation for a storage period which is substantially longer than the period of stimulation. The storage capability of the photoconductive layer 28 is important and will be described hereinafter.

The photoconductive layer 23 may be composed of well-known responsive materials such as cadium sulfide, cadmium selenide, lead sulfide, and many others. The photoconductive layer 28 is preferably highly sensitive and yet not subject to reciprocity failure in order that it may respond to a wide range of luminous inputs from the image cell 10. The photoconductive layer 28 preferably also has a response time sufficiently fast as to not reduce the bandwidth of input video information. The photoconductive layer is preferably formed ofa solid substance, at least the electrical conductivity, capacity or inductance of which varies upon stimulation by photons.

The image-intensifying means includes a second light-emissive device here shown according to the principles of this invention in the form of a luminous gas discharge display cell, which is capable of efficiently producing a high luminous output having a selected spectral characteristic.

In the embodiment illustrated, the display cells 30 each comprise a cylindrical cavity 32 formed in an insulative cavity plate 34. The cavities 32, like cavities 12 in cavity plate 14, may be formed by laser drilling, photoetching techniques, or by any other suitable method.

. The cavity plate 34 is preferably composed ofa suitable material such as ceramic or glass. The lower ends of the cavity 32 are closed by a hermetic seal with the photoconductive layer 28. The photoconductive layer 28 has thereon electrically conductive but optically nonconductive deposits 35 for preventing optical feedback of light emitted by the display cell 30 to the photoconductive layer 28 while allowing passage of electrical current through the display cell 30.

In order to excite the display cells 30, a pair of display electrodes are provided, here shown in the form of a sheet-like intensifier anode 36 and a sheet-like intensifier cathode 38. The anode and cathode 36, 38 for the display cells 30 may, alternatively, comprise rows and columns of discrete electrical conductors, such as the image anode and cathode 20, 22. However, since the element addressing function is provided at the imageforming stage, i.e., in the image cells 10, it is not necessary that the electrodes for the display cells 30 be capable of being individually addressed, to simplify and cost-minimize manufacture, continuous layer electrodes, as shown at 36, 38 are preferred. The anode and cathode electrodes 36, 38 may be composed of an electrically conductive, optically transmissive material such as tin oxide. The anode and cathode 36, 38 may each be deposited during fabrication of the panel by conventional vapor deposition techniques.

In order to optimize efiicency, luminous output and color selectability, the display cells 30 preferably are constructed to operate in a mode termed the positive column" mode. The display cell cavities 32 preferably contain at suitable pressure an ionizable gas such as neon, krypton, xenon or other suitable gas or gas mixture. A compatible light-emitting phosphor selected to have a desired spectral emission characteristic, is deposited on the walls of the cavities 32 for receiving photon energy emitted by the enclosed gas when ionized, and for emitting photons of predetermined wavelengths.

In an application wherein the panel is intended to have a multiple color capability, such as a color television display, the display cells 32 would preferably be arranged in triads, each triad including a red-emitting cell, a blue-emitting cell and a green-emitting cell. The phosphors and associated ionizable gases in each cell are selected to cause the cell to emit light having the appropriate red, blue or green spectral characteristic.

A front cover plate 40, which may be composed of glass or other suitable material completes the panel assembly.

By this invention, the display cell is relieved of imageforming functions and is optimized for luminous efficiency, that is, for luminous output per unit of electrical energy applied, for effective luminance and for color selectability. In a preferred arrangement, in order to optimize the luminous efficiency of the display cell 30, the gas discharge structures comprising the display cells 30 are designed for DC operation. A DC power supply 41 is connected across the intensifier anode and cathode 36, 38 to supply direct current to the display cells.

The image-intensifying means cell 30 and photoconductive layer 28 may be thought of as providing optical gain for the image cell 10. The photoconductive layer may be regarded as a valve or control element which modulates the high luminous output of cell 30 in accordance with the low luminous output of cell 10 which is modulated by the input video signal.

Peripheral circuitry for exciting the image cells 10 will now be described. A row selecting and driving system, hereinafter termed row-drivers 42 and a column selecting and driving system 44 are provided for selectively energizing serially or in parallel the image cells 10. The cells 10 are located at the intersections of the image anodes 20 and cathodes 22.

The row drivers 42 may take any other number of known forms. One conventional approach is to include a shift register which is stepped from one output to the next by a series of gating pulses, in turn initiated by a timing clock that is synchronized by signals coming from a synchronizer, here shown in the illustrated TV application in the form of a sync detector 45 for detecting sync pulses carried by an input video signal. In the illustrated television application, the row drivers 42 se- Iects rows sequentially from top to bottom on the panel 6 as the column selecting and driving system 44 sequentially selects successive columns from left to right.

Alternatively, the row drivers 42 may take the form of switching trees, as is also well known.

In the illustrated embodiment wherein the image cells take the form of gas discharge cells, row selection by the row drivers 42 may be accomplished by applying a negative-going enabling pulse to the selected image cathode 22 of a magnitude which is alone insufficient to exceed the breakdown potential of the image cell 10, but which, when added to a positive-going signal applied to a selected column image anode is sufficient to activate the image cell 10 at the selected rowcolumn intersection.

In accordance with a preferred implementation of the principles of this invention, the column selecting and driving system 44 includes means for sampling the input video signal for an element time and for applying the signal sample to the image cell 10 for a hold period which is substantially longer than the element time, such that the image cell 10 emits a total number of photons which is proportional to an integral of the signal strength sample over the hold period. Sampling and holding the input video signal applied to the image cell 10 has the obvious benefit of increasing the total number of photons emitted by each image cell 10. However, as a practical matter, the sample and hold technique may not be usefully applied in an X-Y matrix display panel to a number of display elements greater than the number of elements in a video line.

On the other hand, to attempt, as some prior art practitioners have, to perform the desired signal holding function by exploiting the persistence of a photoconductive medium is also unsatisfactory, primarily because of the relatively slow response time of the photoconductive materials which are presently available and the degree of stimulation required by these materials.

It is an aspect of this invention to provide a lightemissive element for use in an image display panel which includes a photoconductor responsive to photons emitted by an image-forming cell for controlling an intensifier, which photoconductor is caused to be stimulated for an extended period of time by the use of means for holding the signal sample which is applied to the image cell. The signal sample is applied to the image cell and held for a prolonged period of time, herein termed the hold period, during which the photoconductor is capable of responding fully to photon stimulation. The stimulated photoconductor acts to store the applied signal for a storage period which is substantially longer than the said hold period during which it was stimulated. By this expedient, an effective storage period is obtained which is longer than either the decay time of the photoconductor or the hold period. Further, the full storage capabilities of the photoconductor are realized.

To this end, the column selecting and driving system 44 is shown schematically as including horizontal video sampling switch 46 for sampling a video signal at the output of a video amplifier 48 and for processing the signal samples. The processed signal samples are supplied to memory and column drivers 50 where they are stored in a memory. In the illustrated television application, the memory is capable of serially storing a full line of information. The memory and column drivers 50 includes a storage output switch which dumps the stored information in parallel onto the image anodes 20 (the column electrodes) under the control of a reset and control function 56. The sync detector 45 supplies horizontal sync pulses to the sampling switch 46 and to the reset and control function 56 to synchronize the horizontal and vertical scanning and associated functions.

In the described television application, the photoconductive layer 28 is stimulated for substantially a full line time (typically 50-60 microseconds) rather than being required to respond in an element time as would be the case if the sample and hold system were not provided. Secondly, by the expedient of using an extended stimulation period, rather than a brief high energy pulse of photons, the driving current levels in the panel 6 can be maintained at a relatively low level, making possible the use of low power integrated circuitry for fabrication of the peripheral driving circuits. As is well known, the cost and power consumption of the peripheral circuitry required to drive flat panel displays have been, in a number of cases, the deciding factor against commercial viability. By this invention, sample and hold circuitry is provided for a relatively limited number of display elements, yet the effective period for light emission from the display cell 30 is relatively long.

Sample and hold circuitry suitable for use in the illustrated apparatus is disclosed in US. Pat. No. 3,590,156, assigned to the assignee of the present invention.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broader aspects. For example, in an embodiment wherein the photoconductive means is not responsive to the light emitted by the front display cell, but rather is sensitive to radiation emitted by an appropriately selected image-forming element which does not overlap the spectral characteristics of the display element, the opaque deposits 35 included in the illustrated embodiment need not be provided. The photoconductive layer, may rather than being continuous, comprise discrete areas of photoconductive material, one for each light-emissive element, to assure electrical and optical isolation of the elements. The image and display cells 10, 30 may be physically interconnected and share a common gaseous medium. The aim of the appended claims is, therefore, to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim: 1. In an image display panel for displaying a video signal, a number of light-emissive elements each comprising:

radiation-emissive means capable of emitting radiation in relation to an applied electrical potential;

means for sampling said video signal for an element time and for applying the signal sample to said radiation-emissive means such that said radiationemissive means emits photons in proportion to said signal sample;

photoconductive means optically coupled to said radiation-emissive means and sensitive to said photons, said photoconductive means being characterized by having an impedance which varies with the number of photons impinging thereon and which maintains impedance resulting from photon stimulation for a storage period substantially longer than the period of stimulation;

a luminescent gas discharge display cell electrically connected in series with said photoconductive means for providing a visible light output for said image display panel; and power supply means for establishing an electrical potential across the serially connected combination of said display cell and said photoconductive means, the output of said power supply means being modulated by the variable impedance of said photoconductor for providing said display cell with a source of current which varies in accordance with changes in the impedance of said photoconductive means in response to changes in the level of photon emission by said radiation-emissive means, and thus indirectly in response to variations in the level of said video signal, said photoconductive means acting to store said video signal for said storage period. 2. The element defined by claim 1 wherein said radiation-emission means comprises a gas discharge cell.

3. The element definedby claim 1 wherein said display cell includes phosphors capable of emitting visible light having preselected spectral characteristics.

4. A plurality of light-emissive display elements, in an image display panel, for displaying a video signal each comprising:

radiation-emissive means capable of emitting radiation in relation to an applied electrical potential;

means for sampling said video signal for an element time and for applying the signal sample to said radiation-emissive means for a hold period which is substantially longer than said element time such that said radiation-emissive means emits a total number of photons which is proportional to an integral of the applied signal sample magnitude over said hold period;

photoconductive means sensitive to photons emitted by said radiation-emissive means and characterized by having an impedance which varies with the number of photons impinging thereon and which is I maintained for a storage period substantially longer than the period of photon stimulation thereof, said photoconductive means being optically coupled to said radiation-emissive means such that said photoconductive means is stimulated by photons from said radiation-emissive means for said hold period; a luminescent gas discharge display cell electrically connected in series with said photoconductive means for providing a visible light output for said image display panel; and

power supply means for establishing an electrical potential across the serially connected combination of said photoconductive means and said display cell, the output of said power supply means being modulated by said variable impedance photoconductive means for providing said display cell with a source of current which varies in accordance with changes in the impedance of said photoconductive means in response to changes in the level of photon emission by said radiation-emissive means, and thus indirectly in response to variations in the level of said video signal, said photoconductive means acting to store said video signal for a storage period which is substantially longer than said hold period.

5. The element defined by claim 4 wherein said radiation-emissive means comprises a gas discharge cell.

6. The element defined by claim 5 including means for causing said display cell to be operated in a positive column mode.

7. The element defined by claim 6 wherein said display cell includes phosphors capable of emitting visible light having preselected spectral characteristics.

8. In an image display panel, a plurality of lightemissive elements for displaying a video signal, each comprising in stacked relationship:

a first luminescent gas discharge cell for emitting photons in proportion to an electrical signal applied thereto;

a sample and hold circuit means for sampling said video signal during an element time and for applying the signal sample to said first cell for a hold interval which is substantially longer than said element time such that said cell produces a total number of photons which is proportional to an integral of the applied signal sample magnitude over said hold period; and

light intensifying means, comprising:

a photoconductive layer sensitive to photons emitted by said first cell, said photoconductive layer being characterized by having an impedance which varies with the number of photons impinging thereon and which is maintained for a storage period substantially longer than the period of photon stimulation thereof, said photoconductive layer being optically coupled to said first cell such that said layer is stimulated by photons from said first cell for said hold period;

a second luminescent gas discharge cell electrically connected in series with said photoconductive layer for providing visible light output for said image display panel;

means for optically isolating said photoconductive layer from said second cell; and

power suppply means for establishing an electrical potential across the serially connected combination of said second cell and said photoconductive layer, the output of said power supply means being modulated by said variable impedance photoconductor for providing said second cell with a source of current which varies in accordance with changes in the impedance of said photoconductive means in response to changes in the level of photon emission by said radiationemissive means, and thus indirectly in response to variations in the level of said video signal, said photoconductive layer acting to store said video signal for a storage period which is substantially longer than said hold period.

9. The element defined by claim 8 wherein said second gas discharge cell comprises a fluorescent cell operated in a positive column mode containing phosphors capable of emitting visible light having predetermined spectral characteristics, and wherein said power supply means applies a DC voltage across said second cell.

10. A television display panel for displaying a video signal comprising:

a matrix of light-emissive elements arranged in rows and columns, each comprising:

a first luminescent gas discharge cell for emitting photons in proportion to a signal applied thereto; and

sample and hold circuit means for sequentially sampling a line of said video signal and for simultaneously applying the signal samples to said columns for a hold interval substantially longer than said element sampling time such that each cell emits a total number of photons which is proportional to an integral of the applied signal sample magnitude over the hold period; and

light intensifying means, comprising:

a photoconductive layer optically coupled to said first cell and sensitive to photons emitted by said first cell, said photoconductive layer being characterized by having an impedance which varies with the number of photons impinging thereon and which is maintained for a storage period substantially longer than the period of photon stimulation thereof;

a second luminescent gas discharge cell electrically connected in series with said photoconductive means for providing a visible light output; and

means for optically isolating said photoconductive layer from said second cell;

row selection means for sequentially enabling said rows of elements each for a line time; and

a power supply system for establishing an electrical potential across the serially connected combination of said second cell and said photoconductive layer, the output of said power supply means being modulated by the variable impedance of said photoconductive layer for providing said second cell with a source of current which varies in accordance with changes in the impedance of said photoconductive layer in response to changes in the level of photon emission by said radiation-emissive means, and thus indirectly in response to variations in the level of said video signal, said photoconductive layer acting to store said video signal for a storage period which is substantially longer than a line time.

11. The apparatus defined by claim 10 wherein said second gas discharge cell comprises a fluorescent cell operated in a positive column mode containing phosphors capable of emitting visible light having predetermined spectral characteristics, and wherein said power supply means applies a DC voltage across said second cell.

=k l l 8 i 

1. In an image display panel for displaying a video signal, a number of light-emissive elements each comprising: radiation-emissive means capable of emitting radiation in relation to an applied electrical potential; means for sampling said video signal for an element time and for applying the signal sample to said radiation-emissive means such that said radiation-emissive means emits photons in proportion to said signal sample; photoconductive means optically coupled to said radiationemissive means and sensitive to said photons, said photoconductive means being characterized by having an impedance which varies with the number of photons impinging thereon and which maintains impedance resulting from photon stimulation for a storage period substantially longer than the period of stimulation; a luminescent gas discharge display cell electrically connected in series with said photoconductive means for providing a visible light output for said image display panel; and power supply means for establishing an electrical potential across the serially connected combination of said display cell and said photoconductive means, the output of said power supply means being modulated by the variable impedance of said photoconductor for providing said display cell with a source of current which varies in accordance with changes in the impedance of said photoconductive means in response to changes in the level of photon emission by said radiation-emissive means, and thus indirectly in response to variations in the level of said video signal, said photoconductive means acting to store said video signal for said storage period.
 2. The element defined by claim 1 wherein said radiation-emission means comprises a gas discharge cell.
 3. The element defined by claim 1 wherein said display cell includes phosphors capable of emitting visible light having preselected spectral characteristics.
 4. A plurality of light-emissive display elements, in an image display panel, for displaying a video signal each comprising: radiation-emissive means capable of emitting radiation in relation to an applied electrical potential; means for sampling said video signal for an element time and for applying the signal sample to said radiation-emissive means for a hold period which is substantially longer than said element time such that said radiation-emissive means emits a total number of photons which is proportional to an integral of the applied signal sample magnitude over said hold period; photoconductive means sensitive to photons emitted by said radiation-emissive means and characterized by having an impedance which varies with the number of photons impinging thereon and which is maintained for a storage period substantially longer than the period of photon stimulation thereof, said photoconductive means being optically coupled to said radiation-emissive means such that said photoconductive means is stimulated by photons from said radiation-emissive means for said hold period; a luminescent gas discharge display cell electrically connected in series with said photoconductive means for providing a visible light output for said image display panel; and power supply means for establishing an electrical potential across the serially connected combination of said photoconductIve means and said display cell, the output of said power supply means being modulated by said variable impedance photoconductive means for providing said display cell with a source of current which varies in accordance with changes in the impedance of said photoconductive means in response to changes in the level of photon emission by said radiation-emissive means, and thus indirectly in response to variations in the level of said video signal, said photoconductive means acting to store said video signal for a storage period which is substantially longer than said hold period.
 5. The element defined by claim 4 wherein said radiation-emissive means comprises a gas discharge cell.
 6. The element defined by claim 5 including means for causing said display cell to be operated in a positive column mode.
 7. The element defined by claim 6 wherein said display cell includes phosphors capable of emitting visible light having preselected spectral characteristics.
 8. In an image display panel, a plurality of light-emissive elements for displaying a video signal, each comprising in stacked relationship: a first luminescent gas discharge cell for emitting photons in proportion to an electrical signal applied thereto; a sample and hold circuit means for sampling said video signal during an element time and for applying the signal sample to said first cell for a hold interval which is substantially longer than said element time such that said cell produces a total number of photons which is proportional to an integral of the applied signal sample magnitude over said hold period; and light intensifying means, comprising: a photoconductive layer sensitive to photons emitted by said first cell, said photoconductive layer being characterized by having an impedance which varies with the number of photons impinging thereon and which is maintained for a storage period substantially longer than the period of photon stimulation thereof, said photoconductive layer being optically coupled to said first cell such that said layer is stimulated by photons from said first cell for said hold period; a second luminescent gas discharge cell electrically connected in series with said photoconductive layer for providing visible light output for said image display panel; means for optically isolating said photoconductive layer from said second cell; and power suppply means for establishing an electrical potential across the serially connected combination of said second cell and said photoconductive layer, the output of said power supply means being modulated by said variable impedance photoconductor for providing said second cell with a source of current which varies in accordance with changes in the impedance of said photoconductive means in response to changes in the level of photon emission by said radiation-emissive means, and thus indirectly in response to variations in the level of said video signal, said photoconductive layer acting to store said video signal for a storage period which is substantially longer than said hold period.
 9. The element defined by claim 8 wherein said second gas discharge cell comprises a fluorescent cell operated in a positive column mode containing phosphors capable of emitting visible light having predetermined spectral characteristics, and wherein said power supply means applies a DC voltage across said second cell.
 10. A television display panel for displaying a video signal comprising: a matrix of light-emissive elements arranged in rows and columns, each comprising: a first luminescent gas discharge cell for emitting photons in proportion to a signal applied thereto; and sample and hold circuit means for sequentially sampling a line of said video signal and for simultaneously applying the signal samples to said columns for a hold interval substantially longer than said element sampling time such that each cell emits a total number of photons which is proportional to an integral of the applied signal Sample magnitude over the hold period; and light intensifying means, comprising: a photoconductive layer optically coupled to said first cell and sensitive to photons emitted by said first cell, said photoconductive layer being characterized by having an impedance which varies with the number of photons impinging thereon and which is maintained for a storage period substantially longer than the period of photon stimulation thereof; a second luminescent gas discharge cell electrically connected in series with said photoconductive means for providing a visible light output; and means for optically isolating said photoconductive layer from said second cell; row selection means for sequentially enabling said rows of elements each for a line time; and a power supply system for establishing an electrical potential across the serially connected combination of said second cell and said photoconductive layer, the output of said power supply means being modulated by the variable impedance of said photoconductive layer for providing said second cell with a source of current which varies in accordance with changes in the impedance of said photoconductive layer in response to changes in the level of photon emission by said radiation-emissive means, and thus indirectly in response to variations in the level of said video signal, said photoconductive layer acting to store said video signal for a storage period which is substantially longer than a line time.
 11. The apparatus defined by claim 10 wherein said second gas discharge cell comprises a fluorescent cell operated in a positive column mode containing phosphors capable of emitting visible light having predetermined spectral characteristics, and wherein said power supply means applies a DC voltage across said second cell. 